For example, an exhaust gas recirculation valve (Exhaust Gas Recirculation Valve: EGR valve) provided with a double eccentric valve of the Patent Document 1 mentioned below has been known as this type of technique. This EGR valve includes a valve section consisting of a double eccentric valve. FIG. 12 is a sectional view of a valve section 61 in a valve fully-closed state. FIG. 13 is a sectional view of the valve section 61 in a valve open state in a small opening range. FIG. 14 is a sectional view of the valve section 61 in a valve fully open state. The valve section 61 includes a valve housing 63 provided inside with a passage 62, and in the passage 62, a valve seat 64, a valve element 65, and a leading end portion of a rotary shaft 66 are placed. The rotary shaft 66 has a free end on its distal end provided with a pin 66a and is supported in cantilever configuration by the valve housing 63. The valve element 65 is fixed to the pin 66a. In FIGS. 12 to 14, the passage 62 located on an upper side of the valve seat 64 corresponds to an upstream side of EGR gas flow, and the passage 62 located on a lower side of the valve seat 64 corresponds to a downstream side of the EGR gas flow.
Specifically, as shown in FIGS. 12 to 14, the valve seat 64 of an annular shape includes a valve hole 67 and an annular seat surface 67a formed on an edge of the valve hole 67. The valve element 65 of a circular disc shape includes an annular sealing surface 65a on an outer periphery corresponding to the seat surface 67a of the valve seat 64. The pin 66a has an axis Lp extending in parallel with an axis L1 of the rotary shaft 66 and being positioned eccentrically in a radial direction of the rotary shaft 66. From the valve fully-closed state in FIG. 12 in which the valve element 65 is seated on the valve seat 64, rotation of the rotary shaft 66 about the axis L1 leads to rotation of the valve element 65 in a valve opening direction as shown in FIG. 13, and thus the sealing surface 65a is moved away from the seat surface 67a to open the passage 62. Subsequently, the valve element 65 is further rotated to be in the valve fully-open state as shown in FIG. 14.
The annular valve seat 64 is press-fitted in a step portion 62a formed in the passage 62. Under this press-fitted state, the valve seat 64 has an annular flat upper face 64a located adjacent to the seat surface 67a. The upper face 64a is positioned to face the passage 62. However, a flat lower face 64b of the valve seat 64 does not face the passage 62 since the flat lower face 64b is press-fitted in the step portion 62a. 